1. Field of the Invention
This invention relates to a developing apparatus for an electrostatic latent image or more particularly to a dry type developing apparatus in which single constituent developing agents are used.
2. Description of the Prior Art
Recently the developing methods using single constituent developing agent have been considered to be superior to the conventional 2 constituent developing methods from the points of view of their simplicity, durability, good picture quality, etc. and studies to develop good developing methods are underway. Especially the developing method using insulating toner is spotlighted in that it enables plain paper transcription to be made by the use of corona discharge.
For example, in U.S. patent application Ser. Nos. 58,434 now abandoned and 58,435 now U.S. Pat. No. 4,292,387 by this assignee, examples of apparatus which perform development using such single insulating developing agent are shown. In the developing method using such insulating toner, visualization of latent image is made by coating single constituent developing agent consisting of insulating toner on the toner holding body and making said toner holding body approach or contact the latent image forming body. This method had a great technical problem in the process of coating a thin and uniform toner layer onto the toner holding body. For example, the method in which an elastic coating blade is made to contact with the toner holding body to form a thin toner layer with the travel of the toner holding body is known. However, in this method foreign bodies or condensated toner are easy to block the gap between the elastic coating blade and toner holding body. This gave bad influence on the developed picture by generating white stripes on the section of the toner holding body where the toner was absent. Moreover, the thickness of the toner layer was varied delicately by the contact pressure of the elastic coating blade, resulting in hard control of developing density.